The use of dyes, inks and other chemicals in the colour marking of commercial, consumer and industrial goods places important requirements on supply chains, logistics and the environment. Processes that can colour mark without the use of dyes, inks or other chemicals can therefore provide a distinct advantage.
Laser colour marking has been applied to many materials including metals. Once perfected for a particular material, the laser marking process is typically reliable, repeatable, and amenable to high-throughput high-yield production. An example is the colour marking of anodized aluminum, a material that is in widespread use as it is lightweight, strong, easily shaped, and has a durable surface finish. The anodized surface is generally dyed with coloured dyes. However it is also possible to laser mark anodized aluminum without the use of dyes, inks or other chemicals. Laser light can be used directly to form various colours either within the anodization or in the interface region between the oxide layer that forms the anodization and the aluminum. Similar marks can also be made on other anodized metal surfaces such as titanium, zinc, magnesium, niobium and tantalum.
Copper metal is not readily anodized. Laser marking that relies on an oxide layer is therefore difficult or impossible in copper and alloys such as brass and bronze. Laser marking has been achieved with laser ablation of copper and its alloys to produce colours such as white, black, brown and yellow. However it is not been possible to produce colours such as pink, blue, tangerine, purple, light brown, grey, and orange other than with dyes, inks or with a combination of chemicals and laser marking.
There is a need for a method for laser marking a metal surface with a desired colour that avoids the aforementioned problems.